Optical communications transmitter



Feb. 16, 1965 J. w. OGLAND OPTICAL. coMMumcATroNs TRANSMITTER Filed Deo.18. 1961 INVENToR Jon W. Ogland.

BY y

ATT'oRg 3,170,066 Patented Feb. 16, 1965 3,170,666 t OPTICALCOMNIUNICTIONS TRANSMITTER Jon W. Ogland, Glen Burnie, Md., assigner toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Filed Dec. 18, 1961, Ser. No. 159,881 Claims. (Cl.'250-199) This invention relates to communications apparatus and morespecifically to a transmitter Ifor a communication system which operatesin the optical regionvof the electromagnetic spectrum.

A small concentrated luminous spot can be produced in conventionalcathode ray tubeshaving an instantaneous brightness in the order of amillion foot-lamberts but unless the electron beam producing theluminous spot can be moved around on the phosphor screen, it will burnthe phosphor and even melt a hole inthe glass envelope. Therefore, arather high speed of movement depending upon the energy of the electronbeam is required. Sweeping the beam over the screen such as in the `formof a raster will provide an average area brightness equalptotheinstantaneous spot brightness provided bythe ratio of raster area tospot area. By means of a stationary lens or mirror system this rastermay be focused into a 'small spot of extremely high brightness, but sucha system cannot retain the light energy within a narrow beam fordirection to a distant point. Such direction of light energy to adistant point, for example outer space communication, requires the lightenergy to be emitted from a spot of the smallest dimensions possible`i.e., a point source. One solution to this problem is to keep theelectron gun and beam stationary and rotate the phosphor screen and haveits axis of rotation'moved back and forth whereby the beam sweeps overan annular ring on the phosphor and burning is thereby prevented. Eventhough the screen is moving, the gun is stationary and therefore .theluminous spot is also stationary with respect to the environment. Suchapparatus is described in U.S. patent application Serial No. 159,246,filed December 14, 1961 by R. I. Schneeberger which case is assigned tothe assignee of the present invention.' One diculty which exists withthe apparatus as described by R. l. Schneeberger is that the motor,bearings, and transilatory movement of the phosphor screen is operatedeither at the vacuum of outer space or either the high vacuum inside ofan evacuated envelope. Outgassing of the motor e.g. decomposition andevaporation of insulation `and breakdown of the lubrication for thebearings are particularly diflicult problems which have not beenovercome.

All object of the present invention, therefore, is to provide animproved optical transmitter for providing communications in the regionof the electromagnetic spectrum including ultraviolet, visual andinfrared radiation.

Another object of the present invention is to provide an opticaltransmitter which has a high intensity point source which can beintensity modulated at megacycle rates.

Still another object of the present invention is to provide an improvedoptical transmitter which is especially adaptable for emission ofultraviolet radiation and which can be used for communication betweenextreme distances, such as space vehicles.

Other objects and advantages will become apparent after a study of thefollowing specification when read in conjunction with the accompanyingdrawings in which:

FIGURE l is an illustrative diagram of the preferred embodimentof thepresent invention; and,

FIG. 2 is a diagram further illustrating the preferred embodiment.

The present invention generates a high intensity source of opticalenergy including ultraviolet, visual and infrared radiation by means ofa cathode ray tube which produces a tiny sharply focused spot withoutoverheating and destroying the phosphor while at'the same timepreventing outgassing of the motor and vaporization of the lubricants.This is accomplished by physically rotating the entire cathode ray tubeabout its longitudinal axis and not only the phosphor screen, whilemaintaining the elec- :tron beam deection yoke stationary. Thisarrangement keeps the electron beam and hence the radiated lightVenergysubstantially fixed in space due to the external stationarymagnetic field-while the phosphor coated cathode ray tube-face iscontinuously rotating and bringing cool phosphor areas under the beamexcitation and spinning hot areas away for a cooling oif period. Forexperimental purposes `on the ground, the motor, bearings, and drivemechanism can be kept at ordinary atmospheric pressure. .For'applications` under high vacuum conditions, such as outer space theentire system is kept in an envelope at a gas pressure which does notpose insurmountable lubrication problems.

Referring more particularly to FIG. 1, a cathode ray tube 10 is utilizedwhich is essentially a conventional electrostatic focus, electromagneticdeliection cathode ray tube. Further the tube 1t) is mounted in cradle22 having bearings 75a and 7Gb located at both ends for allowing axialrotation of the tube about its longitudinal axis 13. The electron guncontained in the tube lil comprising the filament 21, the cathode 1'77,the control grid 23, the accelerating electrode 25, first anode 27 andsecond anode 29, moreover is aligned with the bearings 76a and 7611. Thedeflection yoke '24 is held stationary. The cathode ray tube is rotatedby means of a motor 6i) and a rubber disc 64 connected to the motorshaft 65. The rubber disc 64 rests on a spherical disc 62 attached tothe end surface at the neck of the cathode ray tube 10. The sphericaldisc o2, moreover, is connected to the bearing 76h. Rotation of themotor shaft 65 causes the rubber disc 64 to turn which drives thespherical disc 62 rotating the cathode ray tube 10.

All electron beam Ztl is produced in the cathode ray tube itl whose gunelectrodes are connected to slip rings on the outside of the tube neckas follows: the filament 21 is connected to rings 31 and 31a; thecathode 17 is connected to ring 33, the control grid 23 is connected toring 35, the accelerating anode 25 which is internally connected to thesecond anode 29 is connected to ring 37, and the first anode 27 isconnected to ring 39. External power supply voltages, from a source notshown, are supplied to external terminals 90, 92, 94, 9d and lil@ foroperating the filaments, cathode and accelerating electrode and secondanode, the first anode, respectively. Terminal 191 provides an externalconnection to a point of common reference potential 26. The voltagesthus applied to the external terminals are applied -to the respectivetube elements by means of the contacts Si), 32, 34, 3S, and 4t) whichride on slip rings 31, 31a, 33, 37 and 39, respectively.

A luminous spot 19 is produced on the iuorescent screen 1S by means ofthe electron beam 2G. By applying input signalto the input terminal 96which is in turn connected to the control grid 23 by means of the slipring 35 through contact 36, the intensity of the electron beam 2t) ismodulated to produce a light source at the luminous spot 19 varying inbrightness corresponding to the input signal applied thereto.

By keeping the deflection yoke 24 stationary, a deliection voltage isapplied to terminal 57 for maintaining the position of the electron beam2li and consequently the spot 19 substantially stationary with respectto its environment which is moving. An electron tube 44 is utilized inthe ydeliection circuit to control the amount of current flowing in theyoke 24. This is accomplished by connecting one end of the yoke 2d tothe cathode 45 of the electron tube 44 and by connecting the other endto a point of common reference potential 26. In addition, bearings '75aand 78b located in cradle 22 permit tilting of the tube axis ll3 andconsequently the cathode ray tube lll itself. A potentiometer Ell havingone side connected to a negative bias source, not shown, by means ofterminal 5dand having the other side connected to a point of commonreference potential Zoucontrols the deflection current by varying thenegative bias voltage applied to the grid thus varying the plate currentflowing in the electron tube In addition, bearings 73a and 78]) locatedin the cradle 2f?.

permit tilting of the tube axis t3 and consequently the cathode ray tubelil itself. The potentiometer El@ is mechanically linked by means of itsslider 5.2 through the mechanical linkage 74 to the bearing 7811 suchthat the deection current is made to vary inversely proportional to thetilt angle of the cathode ray tube lll. As observed from the outside ofthe cathode ray tube lli, the luminous spot t9 remains stationary evenwhen the tube axis 313 is tilted.

By applying a slowly rocking motion the deliecticn current causesconcentric circles of different diameters or a spiral of predeterminedpitch to be written on the phosphor of the fluorescent screen i3 therebyincreag the utilized phosphor area. Referring to PEG. 2, this rocl'ingmotion is provided by means of the combination of a worm gear 66,circular gear 68, cam '7b and a connecting rod 72 connected to thecradle22. The worm gear 66 is located on the shaft of the motor dll, turningthe cam 7@ providing an upward and downward movement of the connectingrod '72 and the cradle Z2.

ln the present invention shown in FlG. l, the cathode ray tube iti isrotated by means of the stationary motor o@ and the rubber disc 6ft incontact with the spherical disc 62. With a configuration thus provided,the speed of rotation of the cathode ray tube varies in accordance withthe tilt angle provided by the rocking motion previously described. Thisis provided so that the writing speed on the phosphor and its heatingcan be maintained constant.

The phosphor used in the uorescent screen t8 must have a relativelyshort persistence time that is, the time interval wherein brightnesslevel drops to l/lg of its peak value after excitation is removed mustbe very short. This is necessary in order to apply input signals varyingat inegacycle rates. One example is the commercially available P16phosphor whose brightness level drops `to 1/10 of its peak value within2/10 of a microsecond after excitation is removed. When operating in theultraviolet region of the electromagnetic spectrum for which the presentinvention is particularly suitable, the P16 has an even shorterpersistence time for the ultraviolet light it radiates simultaneouslywith the visible light. Also acceptable for ultraviolet application isthe P phosphor. Other available phosphors have even shorter persistenttimes. No phosphors are presently known which emit optical energy in therange, that is called far ultraviolet. Until now there has not been anypractical use for such radiation because it is quickly absorbed in theatmosphere. However, such wavelengths are very suitable for spacecommunication over long distances and would enhance the presentinvention when and if such phosphors become available.

Bearings and sliding contacts are positioned outside the vacuum envelopeof the cathode ray tube lt). Lubricants are available which aresatisfactory at low vacuum, but none seem to work effectively at veryhigh vacuums. For operation in ground based airborne equipment or in thelaboratory these parts operate under familiar environmental conditions.However, when operated in environments such as outer space, the entireapparatus is mounted in a sealed envelope l2 as shown in FIGS. l and 2,containing a gas under pressure sutiicient to eliminate lubricationproblems. A small window d@ is provided in the sealed envelope l2 nearthe position of the luminous spot 19. The light radiation emanating fromthe spot i9 is collected by the optical system ld comprising acassegrainian lens such that light is lirst reflected from reliector l5and then by reilector lo forming the light in a narrow beam fordirection to a distanct point. By providing the sealed envelope l2around the cathode ray tube iti and its associated apparatus the lightenergy must traverse a short distance from the iiuorescent screen l tothe window Ell in a gas medium. When the subject invention is operatedin the ultraviolet region of the optical spectrum a slight absorption issuiered in this gas passage. This loss, however, is minute since thedistance can be made very short and the gas pressure very low.

As already noted the present invention is particularly adaptable for usein the ultraviolet region of the electromagnetic spectrum which oiiersseveral attractive features for space communications that the radioportion of the spectrum lacks. Because the beam width of radiated energyis proportional to frequency, ultraviolet provides vastly increasedenergy concentration. rhis means that longer communication ranges can beobtained with fai' less power and ith much smaller antennas collectorsthan at radio frequency. Both are important considerations for spacevehicles where electric power is at a premium and large antennastructures pose weight and mechanical design problems. The narrow beamwidth which can be a tiny fraction of a degree using modest size optics,such as shown in FlG. l, offers attractive advantage particularly formilitary use, these being communications privacy and comparativesecurity for man made and certain types of natural interference.

in the preferred embodiment of FiG. l the cathode ray tube voltages aresupplied by means of slip rings on the tube neck. lf desired, aconventional tube base may be utilized and the slip rings provided onthe tube socket. Also instead of having bearings at both ends of thecathode ray tube it may be supported by its neel; in suitble bearingssuch as rollers or discs positioned around the tube neck. ln addition,electrostatic focus means have been shown but electromagnetic focus coilmay likewise be utilized outside of the tube instead of theelectrostatic focusing.

in summation therefore, the present invention provides an improved meansfor generating a high intensity point source of radiation for use inoptical communications systems. Whereas previous devices wouldexperience lubrication problems and decomposition due to the vacuumenvironment when operated in outer space the subject invention providesa means in which an optical transmitter can be eticiently operatedeither in the environment of earth or in outer space withoutexperiencing detrimental outgassing and lubrication difficulties.

Accordingly, while there has been shown and described what is at presentconsidered to be the preferred embodiment of the present invention,modifications thereto will readily occur to those skilled in the art. ltis not desired, therefore, that the invention be limited to the specificarrangements shown and described. It should be understood that changesmay be made and equivalents substituted without departing from thespirit and scope of the invention.

i claim as my invention:

l. A transmitter for optical communications comprising in combination: acathode ray tube having a longitudinal axis and including a tluorescentscreen; means operably connected to said cathode ray tube for producinga point source of light at a predetermined spot on said fluorescentscreen; means operable with said cathode ray tube for maintaining theposition of said point source substantially stationary in space; meansconnected to said cathode ray tube for simultaneously axially rotatingand tilting said cathode ray tube about said longitudinal axis; andmeans located adjacent said point source for directing the lightemanating therefrom to an external location. 2. A transmitter foroptical communications comprising in combination: a cathode ray tubehaving a longitudinal axis and including a fluorescent screen; meansoperably connected to said cathode ray tube for producing a point sourceof light at a predetermined spot on said iiuorescent screen; an inputmeans; means connected toV said input means for varying the intensity ofsaid point source in accordance with an input signal; means operablewith said cathode ray tube for maintaining the position of said pointsource substantially stationary in space; means connected to saidcathode ray tube for simultaneously axially rotating and tilting saidcathode ray tube about said longitudinal axis; and means locatedadjacent said point source for directing the light emanating from saidpoint source to an external point.

3. A transmitter for optical communications comprising in combination: acathode ray tube having a longitudinal axis and including a fluorescentscreen; means operaoly connected to said cathode ray tube for generatinga sharply focused point source of licht energy including theultraviolet, the visual, and the infrared regions of the electromagneticspectrum, at a predetermined location on said fluorescent screen;deflection means operable with said cathode ray tube for maintaining theposition of sait. point source substantially stationary with respect tosaid uorescent screen; means connected to said cathode ray forsimultaneously axially rotating and tilting said cathode ray tube aboutsaid lonaitudinal axis; and optical means located adjacent said pointsource for beaming said light energy emitted therefrom to an externalstation.

4. A transmitter for optical communications comprising in combination: acathode ray tube having a longitudinal axis and including a i'luorescentscreen; means operably connected to` said cathode ray tube for producinga spot of light of a predetermined diameter at a predetermined point onsaid fluorescent screen; an input means; means operably connected tosaid input means for intensity modulating said spot of light; meansoperable with said cathode ray tube for detlecting said spot to asubstantially stationary position with respect to an external observer;means connected to said cathode .a ray tube for simultaneously axiallyrotating and tilting said cathode ray tube about said longitudinal axis;and enclosure means including a gas under a predetermined pressureenveloping said cathode ray tube, said means for delecting said spot,and said means for simultaneously axially rotating and tilting saidcathode ray tube for providing a gaseous environment for operation inouter space; and optical means located adjacent said enclosure means fordirecting light emitted from said sot in a relatively narrow beam to adistant point.

5. A transmitter for optical communications in outer space Comprising incombination: a cathode ray tube having a longitudinal axis and includinga fluorescent screen; means operably connected to said cathode ray tubefor producing substantially a point source of light at a predeterminedlocation on said fluorescent screen, means operable with said cathoderay tube for maintaining the position of said point source substantiallystationary in space; means connected to said cathode ray tube forsimultaneously providing axial rotation and tilting of said cathode tubeabout said longitudinal axis in order to dissipate heat produced at saidpoint source; envelope means containing a gas ot a predeterminedpressure disposed around said combination for providing an atmosphere ofpredetermined content for outer space operation, said envelope meansalso including a Window for external transmission of said light emittedfrom said point source; and optical means located adjacent Y said windowfor receiving and beaming said light to a distant point in a relativelynarrow beam.

Reerences Cited in the tile of this patent UNTTED STATES PATENTS2,0%(),670 lartman Nov. 10, 1936 2,681,942 Lubcke June l, 1937 2,403,997Potter luly 16, 1946 2,409,971 Bennett Oct. 22, 1946 2,420,846 Strutt etal. May 20, 1947 2,472,889 Dumont June 14, 1949 2,726,574 lviandler Dec.13, 1955 FOREGN PATENTS 625,165 Great Britain lune 23, 1949

1. A TRANSMITTER FOR OPTICAL COMMUNICATIONS COMPRISING IN A COMBINATION:A CATHODE RAY TUBE HAVING A LINGITUDINAL AXIS AND INCLUDING AFLUORESCENT SCREEN; MEANS OPERABLY CONNECTED TO SAID CATHODE RAY TUBEFOR PRODUCING A POINT SOURCE OF LIGHT AT A PREDETERMINED SPOT ON SAIDFLUORESCENT SCREEN: MEANS OPERABLE WITH SAID CATHODE RAY TUBE FORMAINTAINING THE POSITION OF SAID POINT SOURCE SUBSTANTIALLY STATIONARYIN SPACE; MEANS CONNECTED TO SAID CATHODE RAY TUBE FOR SIMULTANEOUSLYAXIALLY ROTATING AND TILTING SAID CATHODE RAY TUBE ABOUT SAIDLONGITUDINAL AXIS: AND MEANS LOCATED ADJACENT SAID POINT SOURCE FORDIRECTING THE LIGHT EMANATING THEREFROM TO AN EXTERNAL LOCATION.